1. Field of the Invention
The present invention relates to an optical sensor device, and particularly to an optical sensor device configured by a thin film semiconductor element. Further, the invention relates to an electronic apparatus using the optical sensor device.
2. Description of the Related Art
In recent years, cellular phones have been widely used with the advance of telecommunication technology. In future, transmission of moving images and transmission of a larger volume of information are expected. In addition, through reduction in weight of personal computers, those adapted for mobile communication have been produced. Information terminals called PDAs originated in electronic notebooks have also been produced in large quantities and widely used. With the development of display devices, the majority of portable information devices is equipped with a flat panel display.
In such a display device, brightness of the periphery thereof is detected so as to control the display luminance. The suitable display luminance obtained by detecting the peripheral brightness enables power reduction. An optical sensor device for controlling luminance is applied to cellular phones, personal computers, and the like. (e.g., Patent Document 1).
Meanwhile, an optical sensor device is used for the convergence control in a display device having a projector. In the convergence control, an image is controlled so as not to cause the deviation of respective images of each color of RGB. Each image position of RGB is detected to dispose the image at an appropriate position by using an optical sensor. (e.g., Patent Document 2).
These optical sensor devices adopt an amorphous silicon photodiode. Compared to a single crystal silicon photodiode, an amorphous silicon photodiode is less sensitive to the light on the long wavelength side, namely in the infrared region. Respective sensitive characteristics of the amorphous silicon photodiode and the single crystal silicon photodiode are shown in FIG. 13. The amorphous silicon photodiode is less sensitive to the light in the region except the visible light region, which is similar to the human visual sensitivity. On the other hand, the single crystal silicon photodiode is much sensitive even to the light in the infrared region. Therefore, the single crystal silicon photodiode reacts differently from the visual sensitivity in the case where there is some infrared light. This is why the optical sensor device using the amorphous silicon photodiode is suitable for this case.
The above-described optical sensor device configured by the amorphous silicon photodiode has the following problem. As for an amorphous silicon photodiode, output current thereof is smaller than that of a single crystal silicon photodiode while the light sensitivity is close to the human visual sensitivity as mentioned above. Thus, it is difficult for the amorphous silicon photodiode to drive another circuit directly. As illustrated in FIG. 5, the optical sensor device is, consequently, configured by the combination of an amorphous silicon photodiode 502, an external amplifier circuit 501, and a feedback resistor 503 so that output current of the amorphous silicon photodiode 502 is converted into voltage by the feedback resistor 503, which is then outputted from an output terminal 504 as a voltage output.
[Patent Document 1] Japanese Patent Laid-Open No. 2003-60744
[Patent Document 2] Japanese Patent Laid-Open No. 2003-47017